Optical communications networks have recently become established as the preferred backbone for data communications because of the high bandwidth capacity of the optical fiber links. In the modern network space, packetized data traffic of multiple different protocols (e.g. internet protocol, frame relay, asynchronous transfer mode, etc.) is transported over a common network infrastructure. Each protocol provides its own packet (or frame) size and format standards. Additionally, some protocols (e.g. IP) are specifically designed to allow packets having widely varying lengths. New routing protocols, for example the multi-protocol label switching (MPLS) protocol have been proposed to facilitate multi-protocol traffic across a common network infrastructure.
Under the MPLS protocol, label switched packets (LSPs) are propagated across the network hop-by-hop along a path that is set up at the beginning of a communications session. In general, the label assigned to the LSP can be different for each hop, with the label conversion being performed by the node serving the respective hop. Where the network is designed for wave division multiplex (WDM) transport of data traffic, it is desirable to use a data channel (or wavelength) as the label assign to an LSP through a respective hop. In this case, end-to-end transport of an LSP through an MPLS path requires a change of wavelength in the node serving each hop.
However, the modern network space is composed of a mixture of agile cross-connects (i.e. cross-connects capable of wavelength conversion from input to output) and non agile cross-connects (i.e. cross-connects that are unable to do wavelength conversion). Because MPLS normally requires that the labels (i.e. the wavelengths) must be changeable at every hop, non agile cross-connects within the network cannot participate in an MPLS end-to-end optical path. This restriction forces MPLS traffic to be routed around non-agile cross-connects, and serves as a barrier to the widespread implementation of MPLS.
A technique which allows non-agile cross-connects to participate in MPLS end-to-end optical paths is therefore highly desirable.